scholarly journals Electron distribution functions in the electron diffusion region of magnetic reconnection: Physics behind the fine structures

2014 ◽  
Vol 41 (24) ◽  
pp. 8688-8695 ◽  
Author(s):  
N. Bessho ◽  
L.-J. Chen ◽  
J. R. Shuster ◽  
S. Wang
Keyword(s):  
Magnetic Reconnection ◽  
Electron Distribution ◽  
Distribution Functions ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Fine Structures

Observation of non-gyrotropic electron distribution across the electron diffusion region in the magnetotail reconnection

2020 ◽  
Author(s):  
Xinmin Li ◽  
Quanming Lu
Keyword(s):  
Electric Field ◽  
Energy Range ◽  
Electron Distribution ◽  
Distribution Functions ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Vertical Distance ◽  
Magnetospheric Multiscale ◽  
Magnetotail Reconnection ◽  
First Time

<p>Using measurements by the Magnetospheric Multiscale (MMS) spacecraft in the magnetotail, we studied electron distribution functions across an electron diffusion region. The dependence of the non-gyrotropic distribution on the energy and vertical distance from the EDR mid-plane was revealed for the first time. The non-gyrotropic distribution was observed everywhere except for an extremely narrow layer right at the EDR mid-plane. The energy of the non-gyrotropic distribution increased with growth of the vertical distance from the mid-plane. For the electrons within certain energy range, they exhibited the non-gyrotropic distribution at the distance further away from the mid-plane than that expected from the meandering motion. The correlation between the crescent-shaped distribution with multiple stripes and the large Hall electric field was established. It appears that the measured non-gyrotropic distribution and the crescent-shaped distribution were caused by the meandering motion and the Hall electric field together.</p>

scholarly journals Identification of the Electron-Diffusion Region during Magnetic Reconnection in a Laboratory Plasma

2008 ◽  
Vol 101 (8) ◽  
Author(s):  
Yang Ren ◽  
Masaaki Yamada ◽  
Hantao Ji ◽  
Stefan P. Gerhardt ◽  
Russell Kulsrud
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Laboratory Plasma ◽  
Electron Diffusion

Formation of non-thermal electron velocity distribution functions in kinetic magnetic reconnection

2021 ◽  
Author(s):  
Xin Yao ◽  
Patricio A. Muñoz ◽  
Jörg Büchner
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Field Strength ◽  
Magnetic Reconnection ◽  
Electron Beams ◽  
Distribution Functions ◽  
Electron Velocity ◽  
Diffusion Region ◽  
Electron Velocity Distribution ◽  
Velocity Distribution Functions

<div> <div>Magnetic reconnection can convert magnetic energy into non-thermal particle energy in the form of electron beams. Those accelerated electrons can, in turn, cause radio emission in environments such as solar flares. The actual properties of those electron velocity distribution functions (EVDFs) generated by reconnection are still not well understood. In particular the properties that are relevant for the micro-instabilities responsible for radio emission. We aim thus at characterizing the electron distributions functions generated by 3D magnetic reconnection by means of fully kinetic particle-in-cell (PIC) code simulations. Our goal is to characterize the possible sources of free energy of the generated EVDFs in dependence on an external (guide) magnetic field strength. We find that: (1) electron beams with positive gradients in their parallel (to the local magnetic field direction) distribution functions are observed in both diffusion region (parallel crescent-shaped EVDFs) and separatrices (bump-on-tail EVDFs). These non-thermal EVDFs cause counterstreaming and bump-on-tail instabilities. These electrons are adiabatic and preferentially accelerated by a parallel electric field in regions where the magnetic moment is conserved. (2) electron beams with positive gradients in their perpendicular distribution functions are observed in regions with weak magnetic field strength near the current sheet midplane. The characteristic crescent-shaped EVDFs (in perpendicular velocity space) are observed in the diffusion region. These non-thermal EVDFs can cause electron cyclotron maser instabilities. These non-thermal electrons in perpendicular velocity space are mainly non-adiabatic. Their EVDFs are attributed to electrons experiencing an E×B drift and meandering motion. (3) As the guide field strength increases, the number of locations in the current sheet with distributions functions featuring a perpendicular source of free energy significantly decreases.</div> </div>

Micro-scale tearing mode turbulence in the diffusion region during macro-scale evolution of turbulent reconnection

2021 ◽  
Author(s):  
Takuma Nakamura ◽  
Hiroshi Hasegawa ◽  
Tai Phan ◽  
Kevin Genestreti ◽  
Richard Denton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Conversion ◽  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Efficient Energy ◽  
Micro Scale ◽  
Island Evolution ◽  
Macro Scale ◽  
Scale Evolution

<p>Magnetic reconnection is a key fundamental process in collisionless plasmas that explosively converts magnetic energy to plasma kinetic and thermal energies through a change of magnetic field topology in an electron-scale central region called the electron diffusion region. Past simulations and observations demonstrated that this process causes efficient energy conversion through the formation of multiple macro-scale or micro-scale magnetic islands/flux ropes. However, how these different spatiotemporal scale phenomena are coupled is still poorly understood. In this study, to investigate the turbulent evolution of magnetic reconnection, we perform a new large-scale fully kinetic simulation of a thin current sheet considering a power-law spectrum of initial fluctuations in the magnetic field as frequently observed in the Earth’s magnetotail. The simulation demonstrates that during a macro-scale evolution of turbulent reconnection, the merging of macro-scale islands results in reduction of the rate of reconnection as well as the aspect ratio of the electron diffusion region. This allows the repeated, quick formation of new electron-scale islands within the electron diffusion region, leading to an efficient energy cascade between macro- and micro-scales. The simulation also demonstrates that a strong electron acceleration/heating occurs during the micro-scale island evolution within the EDR. These new findings indicate the importance of non-steady features of the EDR to comprehensively understand the energy conversion and cascade processes in collisionless reconnection.</p>

scholarly journals Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

2016 ◽  
Vol 34 (3) ◽  
pp. 357-367 ◽  
Author(s):  
Takuma Nakamura ◽  
Rumi Nakamura ◽  
Hiroshi Haseagwa
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Real Space ◽  
Diffusion Region ◽  
Electron Mass ◽  
Plasma Parameters ◽  
Electron Diffusion ◽  
Background Density ◽  
Spatial Dimensions ◽  
Inner Region

Abstract. Spatial dimensions of the detailed structures of the electron diffusion region in anti-parallel magnetic reconnection were analyzed based on two-dimensional fully kinetic particle-in-cell simulations. The electron diffusion region in this study is defined as the region where the positive reconnection electric field is sustained by the electron inertial and non-gyrotropic pressure components. Past kinetic studies demonstrated that the dimensions of the whole electron diffusion region and the inner non-gyrotropic region are scaled by the electron inertial length de and the width of the electron meandering motion, respectively. In this study, we successfully obtained more precise scalings of the dimensions of these two regions than the previous studies by performing simulations with sufficiently small grid spacing (1∕16–1∕8 de) and a sufficient number of particles (800 particles cell−1 on average) under different conditions changing the ion-to-electron mass ratio, the background density and the electron βe (temperature). The obtained scalings are adequately supported by some theories considering spatial variations of field and plasma parameters within the diffusion region. In the reconnection inflow direction, the dimensions of both regions are proportional to de based on the background density. Both dimensions also depend on βe based on the background values, but the dependence in the inner region ( ∼ 0.375th power) is larger than the whole region (0.125th power) reflecting the orbits of meandering and accelerated electrons within the inner region. In the outflow direction, almost only the non-gyrotropic component sustains the positive reconnection electric field. The dimension of this single-scale diffusion region is proportional to the ion-electron hybrid inertial length (dide)1∕2 based on the background density and weakly depends on the background βe with the 0.25th power. These firm scalings allow us to predict observable dimensions in real space which are indeed in reasonable agreement with past in situ spacecraft observations in the Earth's magnetotail and have important implications for future observations with higher resolutions such as the NASA Magnetospheric Multiscale (MMS) mission.

scholarly journals Electron Bernstein waves driven by electron crescents near the electron diffusion region

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
W. Y. Li ◽  
D. B. Graham ◽  
Yu. V. Khotyaintsev ◽  
A. Vaivads ◽  
M. André ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Hall Current ◽  
Neutral Line ◽  
Electron Velocity ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Field Diffusion ◽  
Bernstein Waves ◽  
Electron Distributions ◽  
Current Reversal

AbstractThe Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth’s magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

scholarly journals Electron Bernstein Waves driven by Electron Crescents near the Electron Diffusion Region

2020 ◽  
Author(s):  
Wenya Li ◽  
Daniel Graham ◽  
Binbin Tang ◽  
Andris Vaivads ◽  
Mats Andre ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Hall Current ◽  
Neutral Line ◽  
Electron Velocity ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Field Diffusion ◽  
Bernstein Waves ◽  
Electron Distributions ◽  
Current Reversal

<p>The Magnetospheric Multiscale spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth's magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. Our analysis shows that the EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.</p>

How does dissipation work in the electron diffusion region of asymmetric magnetic reconnection

2020 ◽  
Author(s):  
Michael Hesse ◽  
Cecilia Norgren ◽  
Paul Tenfjord ◽  
James Burch ◽  
Yi-Hsin Liu ◽  
...  
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Stagnation Point ◽  
Electric Fields ◽  
Current Density ◽  
Electron Flow ◽  
Diffusion Region ◽  
Density Maximum ◽  
Density Peak ◽  
Electron Diffusion

<p>At some level, magnetic reconnection functions by means of a balance between current dissipation, and current maintenance due to the reconnection electric field. While this dissipation is well understood process in symmetric magnetic reconnection, the way nonideal electric fields interact with the current density in asymmetric reconnection is still unclear. In symmetric reconnection, the current density maximum, the X point location, and the nonideal electric field determined by the divergence of the electron pressure tensor usually coincide. In asymmetric reconnection, however, the electric field at the X point can be partly provided by bulk inertia terms, implying that the X point cannot be the dominant location of dissipation. On the other hand, we know that the nongyrotropic pressure-based electric field must dominate at the stagnation point of the in-plane electron flow, and that electron distributions here feature crescents. The further fact that the current density peak is shifted off the position of the X point indicates that there may be a relation between this current density enhancement, the location of the stagnation point, and the electron nongyrotropies. In this presentation we report on further progress investigating the physics of the electron diffusion region in asymmetric reconnection with a focus on how to explain the dissipation operating under these conditions. </p>

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